1. Field of the Invention
This invention relates to an image data compressing apparatus for generating encoding data by subjecting image data representing one frame of an image to calculation of orthogonal transform coefficients, quantization of the orthogonal transform coefficients and encoding of the quantized orthogonal transform coefficients, and storing the generated encoded data in a storage area having a capacity for storing a plurality of frames of encoded data.
2. Description of the Related Art
The motion JPEG (Joint Photographic Experts Group) format is one example of a moving image compression format. According to motion JPEG, image data obtained by subjecting a plurality of frames of still images to JPEG compression is expanded and displayed continuously to thereby present the image data as a moving image. In order to hold the recording time of the moving image substantially constant in such a moving image compression format, it is required that the amount of compressed image data (amount of encoded data) per unit time (one second) be made substantially constant (JP4-203884).
However, if the compression rate of each individual frame is fixed, the amount of compressed image data may change drastically when the scene changes. If this occurs, the amount of compressed image data per unit time cannot be rendered substantially constant.